Combination hydraulic actuator and potentiometer



D. F. SELLERS 3,096,497

COMBINATION HYDRAULIC ACTUATOR AND POTENTIOMETER July 2, 1963 FiledMarch 6, 1961 FIG 2 FIG .3

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INVENTOR.

DONALD E SELLERS AGENT 3,096,497 COMBINATIGN HYDRAULIC ACTUATOR ANDPOTENTIOMETER Donald F. Sellers, Dallas, Tex., assignor, by mesneassignments, to Ling-Temco-Vought, Inc., Dallas, Tex., a corporation ofDelaware Filed Mar. 6, 1.961, Ser. No. 93,410 Claims. (Cl. 338-83) Thisinvention relates to hydraulic actuators and more especially to acombination hydraulic actuator and potentiometer.

Wherever hydraulic actuators are employed, it is frequently necessarythat an electrical device be employed in conjunction therewith forproviding an electrical signal indicative of the position of theactuator piston and hence of the item, for example, an aircraft aileronor other control surface, moved by force exerted by the actuator. Theelectrical signal thus obtained may be utilized for operation of aninstrument giving visual or other indication of the position of theactuator movable element within its range of travel; and an electricalsignal of this kind is indispensable for operation of an electricalsystem for servo control of the actuator. To obtain the electricalsignal, it has been customary to provide a potentiometer for operationwith the hydraulic actuator and to connect the potentiometer movableelement, through a suitable linkage, with a movable element (usually thepiston rod) of the actuator. While such arrangements have made possiblea relatively excellent versatility and precision of servo control ofhydraulic actuators, they have had certain serious disad vantages.Refinement of design and various expedients relating to the mounting anduse of these potentiometers have been carried as far as possible in aneffort to minimize the problems occasioned by these disadvantages, andwhile much inventive skill and craftsmanship have been expended, suchproblems have only been somewhat alleviated thereby and never altogethersatisfactorily solved.

Potentiometers for applications such as mentioned above tend to berelatively expensive in themselves, and their mounting means andespecially the often quite complicated and close-tolerance linkageutilized for their connection to an actuator movable element also addmuch expense. Potentiometers generally tend to be relatively delicate ofconstruction, and unless especially protected are readily injured bychance blows and by mechanical shocks transmitted to them through theactuator or other structure on which they are mounted. Upon installationof the potentiometer, it and/ or its linkage must be rigged and adjustedfor accurate operation in response to movement of the actuator, and thistask is exacting and timeconsuming. Inaccurate rigging or the effects ofvibration, shock, etc. which distort or injure the potentiometer linkageor throw it out of adjustment can result in improper operation of theactuator by the servo control system with results that, in manyapplications, can be very seriously destructive. To alleviate thedangers of mechanical injuries, many potentiometers have been mountedinside the associated actuator; quite effective in protecting thepotentiometer, this expedient at the same time results in greatlyincreased complexity in design, fabrication, assembly and maintenance ofthe actuator and potentiometer.

While it is highly desirable to solve the above and other problems whicharise where a potentiometer is employed in association with a hydraulicactuator, the more general need exists for a more rugged, simplyconstructed, and reliable potentiometer for use in still otherapplications whether or not requiring the operation of a hydraulicactuator,

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Accordingly, it is a major object of the present invention to provide apotentiometer which is sturdy and reliable and not subject to injuryfrom blows and mechanical shocks.

Another object is to provide a potentiometer of simple construction andrequiring no special protection.

A further object is to provide a device usable as a potentiometer andconnectable into a hydraulic system for use either as a hydraulicactuator or as both an actuator and potentiometer.

Yet another object is to provide a combination actuator andpotentiometer which dispenses with linkages between an actuator andpotentiometer and which is not subject to malfunction or failure becauseof improper adjustment of or damage to such a linkage.

Still another object is to greatly simplify and add to the reliabilityof a hydraulic system employing a servocontrolled actuator by providingan actuator which simultaneously serves as a potentiometer and whoseconstruction is of superior simplicity and sturdiness.

Still other objects and advantages will be apparent from thespecification and claims and from the accompanying drawing illustrativeof the invention.

In the drawing,

FIGURE 1 is a View, in longitudinal section, of a potentiometeraccording to the present invention;

FIGURE 2 is a fragmentary view of the potentiometer employing a shuntresistance;

FIGURE 3 is similar to FIGURE 2 but employing an arrangement without theshunt resistance; and

FIGURE 4 is a view, partially schematic showing the potentiometer inlongitudinal section and connected into a hydraulic system for operationas a combination potentiometer and hydraulic actuator.

The linear potentiometer shown in FIGURE 1 includes a vessel or barrelassembly 10 whose cylinder 11 is provided with a pair of caps 12, 13,one on each of its ends. The inner surface 14 of the vessel 10, i.e.,the combined inner surfaces of the cylinder 11 and end caps 12, 13closing off the ends of the cylinder, is non-conductive except in localareas in the region of each end of the vessel. Thus, the cylinder 11conveniently is made of a dielectric material such as a plastic, whilethe end caps 12, 13 are made of a conductive material such as a metal toprovide each with a conductivesurface exposed to the interior of thecylinder. According to a preferred construction, the end caps 12, 13 areof a dielectric material similar to that of the cylinder 11 and each hasbonded or otherwise attached to its inner face a plate of metal or otherconductor. The plates thus provide a first conductive portion 15 of thevessel inner surface 14 which is located in the region of one end cap 12and a second, similar portion 16 in the region of the other cap 13. Thebalance of the inner surface 14 is non-conductive; therefore, itphysically and electrically separates and isolates the two conductiveportions 15, 16 from each other. Of fixed location relative to thevessel 10, the conductive portions 15, 16 shortly will be seen toprovide the two outer ends or terminals of a pair of resistanceelements.

A piston 17 slidably mounted in the cylinder 11 between the twoconductive portions :15, 16 of the vessel inner surface 14 is providedwith suitable sealing means 18 as required for effecting a good sealingoff of the cylinder interior at one side of the piston from that at theother. The piston 17 thus sealingly divides the cylinder interior intotwo variable-volume chambers. It is essential that the two faces 19, 20of the piston 17 be conductive and electrically joined or connectedtogether. This is readily effected by making the piston of metal or, asshown, of a material similar to that of the cylinder 11 and providing onit a pair of metal faces 19, joined by a conductor or conductors such asthe flush rivets 21.

A rod 22 is rigidly attached at its inner end to one side of the piston17 and extends out of the vessel 10 through an opening in one of the endcaps, suitable sealing means 24 being provided at the opening to preventleakage. The rod, preferably made of a dielectric material, has aninternal passage 25 which extends axially of the rod, from a pointalways outside the vessel =10, to the piston 17. Also made of adielectric material, a second rod 23' is attached to the other side ofthe piston 17, extends out of the vessel through a suitably sealedopening in the other end cap 13, and is of the same diameter as thefirst rod 22.

Both chambers are filled, preferably completely, with a conductiveliquid 26 which extends, in each chamber, from a respective end cap 12or 13 to the most nearly adjacent face 19 or 20 of the piston 17. Thus,in each chamber, the liquid forms a resistance element 27 or 28 whoselength is variable by movement of the piston and whose outer-endterminal is an end cap and whose innerend terminal is a face of thepiston. Physically isolated from each other by the piston 17, the tworesistance elements 27, 28 are electrically connected by the pistonfaces 19, 20. As employed herein, the term conductive, which term isalways a relative one,-refers to a degree of conductivity which is highcompared to that of a conventional hydraulic oil, the latter generallybeing an insulator. On the other hand, the term conductive does notinclude herein a conductivity such as that of a storage batteryelectrolyte, whose lack of resistance would defeat the purpose of theinvention. The term is employed with reference to a liquid whoseconductivity is of suitable value for providing, from end to end of theserially connected resistance elements 27, 28, a resistance comparableto that which would be employed, in a given application, in a wire-woundor other conventional potentiometer. To provide a simple and readilyobtainable example of such a liquid, the cylinder is described as filledwith Water containing only the amount of a salt or other ionizingmaterial required for providing the desired degree of conductivity.Other liquids will immediately suggest themselves: for example, aconventional hydraulic oil to which has been added enough finely dividedcarbon or other conductive additive to provide a desired degree of conductivity.

Since the piston rods 22, 23 are the same size, a given motion of thepiston 1'7 reduces the volume of one chamber of the vessel 10 by thesame amount that it increases the other. To permit the motion of thepiston 17 and maintain both chambers of the vessel 10 full, means mustbe provided for allowing the escape of a given quantity of the liquidfrom one chamber with concurrent admission, during motion of the piston17, of an equal quantity of liquid into the other. The barrel assembly10 has two ports 29, 30, one in the region of each of its ends. A tubeend 31 connects into the port 29 and a tube end 32 into the port 30.

A shunt resistance will frequently be required across the potentiometer,and in other cases such a resistance, though not actually required, maybe present Without interfering with the intended operation of thepotentiometer. In both such cases, the tube ends 31, 32 are part of asingle tubular structure (FIG. 2) whose inner surface defines a passageleading out of the vessel 10 in the region of one end cap 12 and backinto the vessel in the region of the other end cap 13. The tubularstructure 33 preferably is of a non-conductive material in order thatthe additional, conductive liquid 34 with which it is filled willconstitute the sole electrical connection between the two ends of thevessel 10 and form a shunt resistance. The same result is obtainable bymaking the tube 33 of a conductive material and providing it with anon-conductive inner coating or layer, and the same applies to thevessel 10, which may be of conductive material whose inner surface islined with an insulating material. The value of the shunt resistance 34is controllable to a desired value by varying the length and diameter ofthe tube 33. Where as high a shunt resistance value as possible isdesired, the tube 33 is made as long and of as small a diameter aspossible without making physical resistance to liquid flow, between theports 29, 39, so high as to unduly slow the rate at which the piston 17can be moved by a normally utilized force applied to one of its rods 22,23. For a lower resistance, the tube 33 is shortened and/or made ofgreater diameter; or a medial portion of the tube is made of aconductive material.

Where no shunt resistance at all is desired, the tube ends 31, 32 arenot interconnected as in FIG. 2 but instead are individually connectedinto respective receptacles such as hydraulic accumulators 35A, 3513(FIG. 3). In this configuration, the materials and/or mounting of thetubes 31, 32 and accumulators 35A, 35B are such that there is noelectrical continuity between the liquid in one accumulator 35A or 35Band that in the other.

The potentiometer further requires means for effecting electricalconnection to the conductive portions 15', 16 of the vessel innersurface 14 and to the piston faces 19, 2%). A device such as theconductor stud 36 (FIGURE 1) extends through the end cap 12 from theconductive portion 15, and a similar stud 37 is provided at the otherend cap 13. A battery 38 or other means for placing an electricalpotential between the conductive surfaces 15, 16 is connected to thestuds 36, 37 as by the pair of leads 39, 40. For connection of thepotentiometer wiper or piston 17 to a position-indicating instrument, aservo control system, etc. a conductor such as a Wire 41 extends intothe outer end of the passage 25 in the piston rod 22 and through thepassage 25 to the piston 17, with both faces 19, 20 of which it iselectrically connected. The dielectric rod 22 electrically isolates theconductor 41 from the surface conductive portion 15 through which itpasses and also from the conductive liquid 26.

One or both the rods 22, 23 is provided with a rod end 42. When the rodend 42 is connected to a body subject to changes in position, the piston17 is moved in one direction or the other by movement of the body andalways has a position in the cylinder 10 which is in accordance With theposition of the body. With the piston 17 centrally positioned in thevessel 10', the conductor 41 provides a signal Whose polarity is midwaybetween that of the two conductive portions 15, 16; as the piston 17 ismoved away from center, the polarity of the signal changes in accordancewith that of the conductive portion 15 or 16 toward which movement ismade by the piston 17 and with the size of the intervals separating thepiston 17 and the respective conductive portions 15, 16. Since both rods22, 23 are of equal diameter, the crosssectional area of each resistanceelement 27, 28 is the same, as is the resistance per given unit oflength of the elements. Consequently, voltage change at the conductor 41in response to movement of the piston 17 tends to be linear.

It will be noted that there is no sliding of a movable Wiper elementalong a resistance wiper or equivalent. Whereas conventionalotentiometers have a fixed resistance element along which a movableelement or wiper slides, the present device employs a pair of resistanceelements 27, 28 with fixed outer ends (defined by the conductiveportions 15, 16) and connected in series at their inner ends by themovable element or piston 17. Physically separated from each other bythe piston 17, the resistance elements 15, 16 change their respectivelengths in accordance with motion of the piston 17. Thus, the onlysliding contacts are between the piston 17 and cylinder 11 and the rods22, 23 and end caps 12, 13. Since these elements readily lend themselvesto a strong and rugged construction, very little wear on them results,and there is no wear at all between the liquid resistance elements 27,28 and potentiometer wiper (piston faces 19, 20). The device, because ofits simple, sturdy construction, is well able to withstand blows,vibration, and shocks which would prove injurious to otherpotentiometers; it needs no special protection of the kind which must begiven the more delicate, conventional potentiometers. Because of thissimplicity and sturdiness, the potentiometer is of high reliability. Thevoltage output of the potentiometer is continuously variable with wiperposition and is not subject to the resolution deficiencies of wire-woundpotenti-onieters. While thus of excellent usefulness as a potentiometer,the device, as will now be explained and described, is connectable intoa hydraulic system for operation as both an actuator and potentiometer.

The vessel A of FIGURE 4 is similar to that already described inconnection with FIGURE 1, or (as shown) it may employ metal end caps12A, 13A. The piston 17A also is of metal; thus, the piston faces 19A,29A as well as the end cap inner surfaces 15A, 16A are conductive. Wherea linear potentiometer is desired, two equaldiameter piston rods may beemployed as in FIGURE 1. Where a non-linear operation is required, oneof the two rods is of smaller diameter than the other, or (as shown) oneis omitted altogether. The device is used in conjunction with ahydraulic system comprising a reservoir 43 containing the sameconductive liquid 26 that fills the barrel assembly and which suppliesthe liquid to a pump 44. The latter has a port or outlet 45 to which itsupplies the liquid 26 under pressure.

Connecting means for conducting the liquid 26 comprise hydraulic lines46, 47 connected between the barrel assembly ports 29A, 30A and thereservoir 43 and pump 44. Depending on the desired mode of operation ofthe vessel 10A and piston 17A as a hydraulic actuator, a valve 48 isinterposed in one or both of the lines 46, 47 from the pump 44 andreservoir 43 to control the admission of the conductive fluid 26 to thevessel 10A. As a typical example, the four-way valve 48 connects thepressure line 47 from the pump 44 to the tube 32A leading to the port30A at the right-hand end of the vessel and the return line 46 to thetube 31A leading to the other port 29A; or the valve setting is changedto reverse these connections as desired. To prevent a direct shortacross the potentiometer, a resistance must be introduced between theseports 29A, 30A. For this purpose, at least one of the tubes 31A, 32Aleading into the ports 29A, 30A is made of a non-conductive material,thus providing, in the connecting means, a segment, for example the tube31A, within the length of which only the liquid 26 is conductive. Of theconductive liquid 26 additional to that in the vessel, the additionalliquid being contained in the hydraulic lines 46, 47 with subjoinedtubes 31A, 32A and in the reservoir 43 and pump 44, it is the liquidwithin the non-conductive tube 31A (or tubes 31A, 32A) connected to theports 29A, 30A which provides and establishes the shunt resistance valuebetween the ports.

Leads 39A, 40A and a conductor 41A strung through the piston rod 22A areemployed as before to effect electrical connection to the conductiveportions 15A, 16A of the barrel assembly inner surface 14A and to thepiston faces 19A, A.

Upon the conductive hydraulic liquid 26 being supplied by the pump 44 toone of the ports 29A or 30A, the resulting motion of the piston 17Aforces an equivalent amount of liquid out the other port 29A or 36A andinto the return line 46. A body (for example, an aircraft controlsurface) connected to the piston rod end 42A is moved by displacement ofthe piston 17A. The voltage on the conductor 41A varies, as alreadyexplained, with the position of the piston 17A relative to the conductorportions 15A, 16A. Thus, the device operates as a combination hydraulicactuator and potentiometer. All linkages formerly necessary between ahydraulic actuator and a potentiometer are eliminated, as is alllikelihood of malfunction or failure because of improper adjustment ofor damage to such a linkage. Much simplification also is efiectedandreliability is increased by eliminating the linkage and also byobviating the necessity for mounting and protecting a separatepotentiometer. Since, in the particular example shown in FIG- URE 4, oneresistance element 27A has its cross-sectional area reduced by thepresence of a piston rod 22A while the other element 28A does not, therate of change in resistance value accompanying movement of the piston17A through a given distance is greater in the resistance element 27Athan in the other. As a consequence, the action of the potentiometer, asto the voltage supplied by the piston 17A to the conductor 41A, isnon-linear; and the extent of the non-linearity may be increased ordecreased as desired by increasing or decreasing the diameter of the rod22A or eliminated altogether by providing tw-o equal-diameter rods as inFIGURE 1.

While only one embodiment of the invention, together with modificationsthereof, has been described in detail herein and shown in theaccompanying drawing, it will be evident that various furthermodifications are possible in the arrangement and construction of itscomponents without departing from the scope of the invention.

I claim:

1. A potentiometer comprising: a vessel having an inner surface andincluding a cylinder and a pair of end caps closing off the ends of thecylinder; a portion of said inner surface in the region of one and aportion of said inner surface in the region of the other of the endcaps, said portions being conductive and the balance of the innersurface being non-conductive and electrically isolating the conductiveportions from each other; means for effecting electrical connection toeach conductive portion; a piston slid-ably mounted in the cylinder anddividing the vessel into two chambers, the piston having conductive,electrically connected faces; a conductive liquid filling both chambers,the liquid in one chamber being electrically connected to the liquid inthe other by the piston faces and the conductive faces beingelectrically connected through the liquid in the chambers and the pistonfaces; a conductor connected to the piston faces and electricallyisolated from the liquid and the conductive surfaces, said conductorhaving an end extending outside the vessel; and material having anon-conductive inner surface defining a passage leading out of thecylinder in the region of one of the end caps and back into the cylinderin the region of the other of the end caps, the passage being filledwith the conductive liquid.

2. A linear potentiometer comprising: a vessel having an inner surfaceand including -a cylinder and a pair of end caps instrumental in closingoff the cylinder ends, each end cap having an opening therethrough; aportion of said inner surface in the region of one and a portion of saidinner surface in the region of the other of the end caps, said portionsbeing conductive and the balance of the inner surface beingnon-conductive and electrically isolating the conductive portions fromeach other; means for effecting electrical connection to each conductiveportion; a piston slidably mounted in the cylinder and dividing thevessel into two chambers, the piston having conductive, electricallyconnected faces; a first dielectric rod of given cross-sectional areaconnected to one side of the piston and extending out of the vesselthrough the opening in one of the end caps; a second dielectric rod ofthe same cross-sectional area as the first connected to the piston andextending out of the vessel through the opening in the other end cap; aconductive liquid filling both chambers, the liquid in one chamber beingelectrically connected to the liquid in the other by the piston facesand the conductive surfaces being electrically connected through theliquid in the chambers and the piston faces; a conductor connected tothe piston faces and electrically isolated from the liquid and theconductive surfaces, said conductor having an end extending outside thevessel; and means keeping the vessel full of the conductive liquid uponsliding of the piston in the vessel.

3. A potentiometer comprising: a vessel having an inner surface andcomprising a cylinder with closed ends; a first, conductive portion ofsaid inner surface in the region of one and a second, conductive portionof said inner surface in the region of the other of the ends of thevessel and exposed to the interior of the vessel in fixed locationrelative to the same; a piston with electrically joined, conductivefaces mounted in the cylinder and dividing the same into first andsecond chambers; first and second resistance elements physicallyisolated from each other and electrically connected by the piston, eachof said elements including a conductive liquid filling a respective oneof said chambers and extending between a respective one of theconductive surfaces and the piston; an electrical shunt resistanceacross said elements and including conductive liquid contained in apassage having one end opening into one of the chambers and another endopening into the other of the chambers adjacent the cylinder ends.

4. A combination hydraulic actuator and potentiometer comprising: abarrel assembly having two end caps and an inner surface; a firstconductive portion of said inner surface in the region of one and asecond conductive portion of said inner surface in the region of theother of the end caps; a non-conductive portion of the inner sur faceextending between and electrically isolating said conductive portionsfrom each other; a piston s-lidably mounted in the barrel assemblybetween the conductive portions and sealingly dividing the barrelassembly into two chambers, the piston having conductive, electricallyconnected faces; :a dielectric rod connected to the piston and extendingoutside the barrel assembly through one of the end caps, the rod havingan internal, axially disposed passage extending from the region of thepiston to a point outside the barrel assembly; a conductor connected tothe piston faces and extending outside the barrel assembly through thepassage of the rod; a conductive liquid filling both chambers of thebarrel; a port in each end of the barrel assembly whereby conductiveliquid may be forced into and discharged from the barrel assembly foreffecting movement of the piston and rod; and means for effectingelectrical connection to each conductive portion for placing anelectrical potential between them.

5. In combination, a reservoir; a conductive liquid contained by thereservoir; a pump having an outlet and receivingly connected to thereservoir for sup plying the conductive liquid, under pressure, at theoutlet; a vessel having an inner surface and comprising a cylinder withclosed ends; a first conductive portion of said inner surface in theregion of one and a second conductive portion of said inner surface inthe region of the other of the ends of the vessel and exposed to theinterior of the vessel in fixed location relative to the same; a pair ofelectrical connecting means, one means being connected to the first andthe other means to the second of said conductive surfaces; means placingan electrical potential between said electrical connecting means; apiston with electrically joined, conductive faces mounted in thecylinder and sealing-1y dividing the same into first and secondchambers; a conductor connected to the piston faces and having an endextending outside the vessel, the conductor being electrically isolatedfrom the conductive liquid and the conductive surfaces; 21 port in eachend of the vessel; and connecting means comprising hydraulic linesconnected between the vessel ports and the reservoir and pump outlet, atleast one of said lines including a non-conductive segment leading intoa respective one of the ports of the vessel.

References Cited in the file of this patent UNITED STATES PATENTS

1. A POTENTIOMETER COMPRISING: A VESSEL HAVING AN INNER SURFACE ANDINCLUDING A CYLINDER AND A PAIR OF END CAPS CLOSING OFF THE ENDS OF THECYLINDER; A PORTION OF SAID INNER SURFACE IN THE REGION OF ONE AND APORTION OF SAID INNER SURFACE IN THE REGION OF THE OTHER OF THE ENDCAPS, SAID PORTIONS BEING CONDUCTIVE AND THE BALANCE OF THE INNERSURFACE BEING NON-CONDUCTIVE AND ELECTRICALLY ISOLATING THE CONDUCTIVEPORTIONS FROM EACH OTHER; MEANS FOR EFFECTING ELECTRICAL CONNECTION TOEACH CONDUCTIVE PORTION; A PISTON SLIDABLY MOUNTED IN THE CYLINDER ANDDIVIDING THE VESSEL INTO TWO CHAMBERS, THE PISTON HAVING CONDUCTIVE,ELECTRICALLY CONNECTED FACES; A CONDUCTIVE LIQUID FILLING BOTH CHAMBERS,THE LIQUID IN ONE CHAMBER BEING ELECTRICALLY CONNECTED TO THE LIQUID INTHE OTHER BY THE PISTON FACES AND THE CONDUCTIVE FACES BEINGELECTRICALLY CONNECTED THROUGH THE LIQUID IN THE CHAMBERS AND THE PISTONFACES; A CONDUCTOR CONNECTED TO THE PISTON FACES AND ELECTRICALLYISOLATED FROM THE LIQUID AND THE CONDUCTIVE SURFACES, SAID CONDUCTORHAVING AN END EXTENDING OUTSIDE THE VESSEL; SAID CONDUCTOR HAVING ANON-CONDUCTIVE INNER SURFACE DEFINING A PASSAGE LEADING OUT OF THECYLINDER IN THE REGION OF ONE OF THE END CAPS AND BACK INTO THE CYLINDERIN THE REGION OF THE OTHER OF THE END CAPS, THE PASSAGE BEING FILLEDWITH THE CONDUCTIVE LIQUID.